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Abstract

The bulk thermal conductivity (TC) of 26 rock samples representing felsic, intermediate and mafic granulites, from the Southern Granulite Province, India, is measured at dry and saturated conditions with the optical-scanning method. Thermal conductivity is also calculated from modal mineralogy (determined by XRD and EPMA), applying mixing models commonly used in thermal studies. Most rocks are fine- to medium -grained equigranular in texture. All samples are isotropic to weakly anisotropic and possess low porosities (< 2%). Measured TC values range between 2.5 and 3.0 W/(mK) for felsic granulites, between 2.5 and 3.5 W/(mK) for intermediate granulites and between 2.4 and 2.7 W/(mK) for mafic granulites. Considering this data and literature compilations, rocks representative for the lower continental crust typically display values between 2 and 3 W/(mK) at ambient temperature and pressure conditions. If corrected for temperature and pressure, this interval translates into in-situ TC values that are between several 0.1 and 1.0 W/(mK) lower depending on type of continental setting. Depending on the mixing model and the mineral TC value used in the calculations, measured bulk TC could be satisfactorily reproduced. Taking advantage of mean values of mineral TCs, the harmonic mean provides an almost perfect fit, with a mean deviation of −1 ± 6% (1sd). However, the implication of that correspondence would be that minerals and pores are predominantly aligned parallel, which is in apparent contrast to the texture of the rocks. The geometric mean, which does not consider any layering of minerals or pores and, thus, should be in better harmony with the textural characteristics of the rocks from this study, matches the measured TC data similarly well (mean deviation 5 ± 8%), if minimal mineral TCs reported in the literature are applied. Thus, if appropriate samples (in terms of sample size or physical-chemical-mechanical condition) for laboratory measurement are not available, bulk TC of high-grade metamorphic rocks with low anisotropy and porosity could be satisfactorily good assessed from modal mineralogy, using the data sets for mineral TC applied in this study.